A koi quarantine tank is sized by the shipment, not by the tank catalogue. Thirty koi at 1.5 Kg carry 45 Kg, which needs 2,250 to 4,500 Liter at 10 to 20 Kg per 1,000 Liter, or four to nine published tanks. It also has to cycle four to six weeks before the fish land, because the filter must carry the day-one load. A tank that shares water, air or nets with the main pond is not a quarantine, whatever its volume.
The batch sets the volume, not the tank
Koi quarantine tank size per fish is quoted as a range, and ranges hide the arithmetic. A 30-fish shipment of 1.5 Kg koi carries 45 Kg of biomass: 4,500 Liter at 10 Kg per 1,000 Liter, 2,250 Liter at 20 Kg, and the gap is the difference between four and nine tanks of the published sizes, 500 to 1,200 Liter. One 1,200 Liter unit holds 12 Kg at the cautious end and 24 Kg at the aggressive end.
Floor area follows: the largest published footprint is 300 by 80 Cm, or 2.40 M2, so a four-tank room loses 9.6 M2 before aisle, filter or work table.
Why the system has to cycle before the fish land
A koi quarantine tank setup is judged by its commissioning date, not its equipment list. A filled tank is not a filter: nitrifying bacteria typically colonise over four to six weeks at 24 C, and a tank filled the week before landing cannot convert the ammonia the batch produces on day one. It needs a fishless cycle on a measured ammonia source, a nitrite reading that rises then falls, and a filter that still converts under the full batch load.
Water preparation runs a second clock: chlorine must read zero before fish enter, and temperature must sit at the holding point rather than drift toward it.
Two ways to hold a batch, and what each one shares
Koi quarantine biosecurity is decided by what the tank shares, not by what it filters.
Table 1. Two koi quarantine tank options compared for a 45 Kg batch
Assumptions: 30 koi at 1.5 Kg; 10 to 20 Kg per 1,000 Liter. Sources: published tank volumes and sizes.
Scheme A is a room with its own water, air and tools. Scheme B is a koi tank on the sales floor, on its own circuit but in the same air as the display system. The difference matters because koi herpesvirus is shed in faeces, urine, gills and skin, and WOAH records it viable in water for at least 4 hours and less than 21 hours at 23 to 25 C; a splash, a shared net or a bucket carries it further than water.
Ruibit publishes a 600 to 1,000 Liter aluminum frame koi tank from 80 by 80 by 145 Cm, with double filtration and a 7-day lead time; the page publishes 5 W or 10 W and no flow figure, so turnover has to be requested as a pump duty point.
How long to quarantine imported koi, and at what temperature
WOAH sets the floor at four weeks and suggests up to two months before new fish mix with naive stock, with sentinel fish held at a permissive temperature (Aquatic Manual, chapter 2.3.6, section 2.4.7). Temperature is not a detail: clinical signs appear 3 to 21 days after exposure, disease occurs mainly between 16 and 29 C, and inspection is only meaningful above 16 C.
The tank therefore has to support a choice: holding at 12 to 14 C suppresses expression, so the batch looks clean and proves nothing; holding at 20 to 25 C lets disease appear inside the window, which needs a heater sized for the room, not the water.
A clean window is evidence, not a certificate: survivors can stay persistently infected and shed later (section 2.2.5).
Ammonia is read three ways, and pH is one of them
Table 2. Free ammonia as a share of total ammonia nitrogen, by pH and temperature
Calculated from the ammonia equilibrium relationship in Emerson et al. (1975), pKa = 0.09018 + 2729.92/T, as a share of total ammonia nitrogen.
A total ammonia reading is not a toxicity reading. At 20 C, 1.2 Percent of total ammonia nitrogen is free ammonia at pH 7.5 and 11.1 Percent at pH 8.5, so the same 1.0 mg per Liter figure means different things in soft planted water and in hard water after a buffer addition. Hence ammonia, nitrite, pH, KH and a thermometer, with pH and temperature written beside every ammonia figure: a meter that logs ammonia alone cannot be interpreted.
When the smaller scheme is the right one
Scheme B is right under three conditions at once: the batch stays below 24 Kg, which one 1,200 Liter tank holds at 20 Kg per 1,000 Liter; the room holds no other carp; and the drain leaves the building rather than feeding a shared sump. Above 24 Kg, or with two shipments overlapping, the room stops being optional, because a second batch cannot wait for the first to clear.
On either scheme the order goes in before the fish: tank, filter, heater, air, test kit and a drain that does not return to the pond.
FAQs
1. How big must a koi quarantine tank be?
Thirty koi at 1.5 Kg carry 45 Kg, needing 2,250 to 4,500 Liter at 10 to 20 Kg per 1,000 Liter. One 1,200 Liter tank holds 12 to 24 Kg.
2. How early must the system be running?
Four to six weeks. A tank filled the week before cannot convert ammonia on day one.
3. Is a sales floor tank enough?
Only if the batch stays below 24 Kg, no other carp in the room, and the drain leaves the building.
4. How long should imported koi stay isolated?
Four weeks minimum, up to two months, at a temperature that lets disease show; signs appear in 3 to 21 days.
5. Why log pH beside ammonia?
At 20 C, 1.2 Percent of total ammonia nitrogen is free at pH 7.5 against 11.1 Percent at pH 8.5.
